1. Technical Field
The present invention relates to an information display apparatus which superimposes, for display, information for display onto images captured in time sequence, and more particularly, a technique to improve performance of the entire apparatus, efficiently making use of a cache memory.
2. Background Art
Apparatuses have been known which superimpose, onto a captured image, information obtained from an information source (a light source) in an imaging range via a visual light communication with the use of an image sensor to display the resultant image to a user. Patent Literature 1 describes that presentation information as a result of change of brightness, the content of which is relevant to goods or an advertising display, is transmitted from an information source attached to a shelf for the goods at a store, the advertising display in the city, or the like, an imaging device captures images in time sequence, extracts respective presentation information from the change of brightness for each image region, superimposes the extracted presentation information onto the respective captured images, thereby clarifying the correspondence between the goods of the information presentation and the presentation information, and a misunderstanding in information recognition is eliminated.
Such an imaging device, however, can acquire information only from an information source (a light source) that has entered the imaging range. Thus, if the information from the light source is large in size, a user has to wait a predetermined period of time from the image capturing to the superimposition of the information onto the image for display. In a case where a camera operator takes images while moving, the imaging range changes and dropout of the information source occurs frequently. When the imaging range changes and a new information source is captured, communication processing occurs, and, naturally, the imaging device cannot display presentation information regarding the new information source until the processing completes.
On the other hand, if the same information source frequently falls in and out of the imaging range, the communication processing occurs to acquire the same information each time the information source enters the imaging range, which causes waiting time. Consequently, a problem occurs that performance of the entire apparatus is undesirably degraded. To solve such a problem, a method is known in which, for example, presentation information, which is acquired from an information source when the information source enters the imaging range, is saved in a cache memory even after the presentation information falls out the imaging range, and when the same information source enters the imaging range, the presentation information is loaded from the cache memory for reuse.
Also, a wireless optical transmission system which allows high-speed and accurate adjustment of an optical axis is disclosed in Patent Literature 2. Patent Literature 2 describes that a master device attached to the ceiling or the like controls and transmits narrow directional light for signal transmission and wide directional light for the optical axis alignment on the same axis, and a wireless optical transmission apparatus on a desk or the like locates the master device at a high speed by a first direction detection section, and locates the master device at a high accuracy by a second direction detection section, thereby downscaling the apparatus without raising cost, and able to perform the high-speed and high-accuracy adjustment of the optical axis in an optical communication.